i did a quick search and see that there are 2 separate plates in the 63-68 water pump plates . I do not have any experience with that style. the 11 bolt ones use a regular fibre gasket between the plate and the pump and another between the plate and timing cover. the clearance check is done with the gasket in place. you measure the gap between the impeller and the edge of the divider plate. i see the 63-68 ones do not have the bolt holes in the them so they must not require any gasket between them and the mounting surfaces. they do have the same surface that goes up against the impeller though so I would imagine the clearancing is still important.